1. Field of the Invention
The present invention relates to improvements in the on-site filtering of cooking oil of the type held in vats of deep fat fryers used in cooking establishments such as in restaurants, donut making and bakery operations and the like. The filtering of the edible cooking oil is intended to remove small solid particles from the oil to extend its useful life for economic and environmental reasons.
2. Description of the Prior Art
It is known that the edible cooking oil in a deep fat fryer vat accumulates solid impurities from the foods cooked therein, the solid impurities charring (carbonizing) and continually breaking into smaller particles with heat and time, and leading to food cooked in the oil not tasting and smelling as good as it otherwise could have had the oil been clean, as described in U.S. Pat. No. 5,160,444 issued Nov. 3, 1992 to G. E. McFarland for Cooking Oil Filtering Method and Apparatus. The McFarland patent 5,160,444 is currently assigned to the same Assignee of the present invention, and is herein incorporated by reference for both essential and non-essential information. The McFarland patent is incorporated primarily but not exclusively for its descriptions of filter containing canisters, conduits feeding cooking oil to the canisters and filtered oil away from the canisters; canister and filter shapes, and seals to ensure the impurity laden oil passes through the filter element; oil filters removably contained within the canisters; the openable lids on the canisters which allow removal of the filters; the fluid tight nature of the canister lids in the closed condition; the use of a pressure gauge to sense when the filter is creating excessive back pressure; the use of a motorized fluid pump to forcefully move the cooking oil through conduits, filters and back into the fryer vat; and for the mounting of the filtering apparatus on wheels. The present invention seeks to overcome major shortcomings in the McFarland invention and other related prior art cooking oil filtration systems.
It is not uncommon in a busy restaurant or donut making operation for the deep fat fryer cooking oil to become contaminated with solid impurities in a single day beyond that which allows the oil to be properly used the following day unless the oil is effectively cleaned such as by filtering to remove at least some of the impurities. Prior art cooking oil filtering processes and apparatuses have been developed for on-site cleaning of the oil in a deep fat fryer vat in an attempt to extend the useful life of the cooking oil, although none are the same or as effective as the present invention at addressing the problems associated with deep fat fryer oil. Most if not all of the prior art cooking oil on-site cleaning arrangements employ the use of disposable filters of cloth, paper, wound cotton string, diatomaceous earth, and sometimes large mesh wire screens used as large chunk pre-filters or screens in combinations with finer disposable filtering materials such as paper, wound cotton string and the like. In most all oil filtering using these prior art filters, the cooking oil is moved through the filter in a warm state so that the oil is liquified, or not congealed. The disposable oil filters of the prior art have very short useful lives, as they clog with the impurities removed from the oil, and are not sufficiently durable to allow proper cleaning for re-use, although some woven cloth filters may be washed and reused a couple of times. Additionally, prior art cooking oil filtering arrangements often only extend the life of the oil for between four and seven days, after which the oil is sent to an oil reclamation facility at the expense of the cooking facility operator. With the McFarland device using three wound cotton string filters connected in series and with daily filtering, the life of the oil can be greatly extended, however the larger porosity disposable filters for filtering down to 5 and 1 micron require replacement every couple of days depending upon the condition of the oil, and the 0.5 micron filter used by McFarland requires replacement after only a few minutes of filtering dependant upon the condition of the cooking oil being filtered. If the McFarland 0.5 filter is not changed when it becomes clogged with entrained solid impurities, the pressure required to push the oil through the very fine filter will cause the string of the filter to part or separate wherein the oil will pass through the filter without any further filtering. This filter parting to allow oil to pass without any further filtering also occurs with the 5 and 1 micron filters used in the McFarland apparatus if these filters are not changed after collecting of a significant amount of solid particles. Another significant drawback found in the McFarland device was that the wound cotton string began to char at about 200 degrees fahrenheit, which is well below the operating temperature of fat fryer cooking oil. Wound cotton string filters require replacement at what is considered to be an excessive frequency, are not suitably structured to allow cleaning and reuse and thus are disposable, and begin charring at a relatively low temperature.
Furthermore, in many if not all states of the U.S., cooking oil and disposable equipment containing significant amounts of the cooking oil, such as disposable oil filters for example, must be handled similar to hazardous waste. Such special handling of oil and contaminated filters costs a significant amount of money, and thus, between the cost of emptying and then refilling the fryer vat with new clean oil every few days, and the special handling requirements associated with discarding of the impurity laden oil and disposable filters, the maintenance of good clean cooking oil in the deep fat fryers in a restaurant or like large scale cooking operation is currently quite substantial.
Additionally, since many large scale kitchen operators are not aware that they are not supposed to, or that it is environmentally unsound to dispose of disposable cooking oil filters simply by throwing them into the garbage to be hauled to the local landfill, many disposable filters saturated with cooking oil end up in the landfill leaching oil into the ground, ground water and streams.
With filtering cooking oil utilizing prior art filtering arrangements, particularly those utilizing single stage disposable filters, the useful life of the oil is not significantly extended, as many filtering systems currently on the market advertise that they can extend the useful life the oil for four to seven days with daily filtering. This relatively short extension of the useful life of the oil is in most cases due to the relatively large porosity of the disposal filters, and the delicate nature of such filters which limits the fluid pressure or suction which may be applied to move the oil through the filter without the filter collapsing, tearing or otherwise coming apart and opening up to allow unfiltered oil to pass. This delicate nature of the prior art disposable filters generally requires a relatively large porosity, particularly when used in a single stage filtration, since high pressure cannot be applied, at least not for an extended period, to push the oil through the filter, thus often times commonly disposable filters are designed to filter out solid particles down to only about 30 to 50 microns, and usually if not always with the cooking oil substantially below cooking temperature to avoid filter charring.
Numerous different types of edible king oils are employed in deep fat fryers as determined by factors including cost of the oil, saturated fat and other health and nutrition concerns, taste of the oil, and desired operating temperature for particular types and classes of foods to be cooked in the oil. These different types of oils which include animal fat, palm oil, peanut oil, safflower oil, canola oil and combinations thereof to name just a few, all have varying burn temperatures and thus maximum operating temperatures. Depending upon the oil used in a deep fat fryer vat, and the wishes of the chef, deep fat fryers are operated at varying temperatures ranging anywhere between 325 to 400 degrees fahrenheit. Disposable filtering materials such as some of the paper and cloth-like materials such as the wound cotton style filters will char at the normal oil operating temperatures which can by itself add an undesirable taste and color to the oil during filtering with such filters. In order to avoid such filter charring, the oil must be filtered prior to the oil reaching operating temperature, or it must be allowed to cool substantially before filtering, which is oftentimes inconvenient since the oil will not cool down rapidly simply by dissipating heat into the ambient air around the vat, which is the normal process of cooling the hot oil. An additional possible inconvenience, depending upon the particular situation, is that during the cooling of the cooking oil, the fryer is out of service, and this might be particularly undesirable in a restaurant which is open 24 hours a day and which only has one or two fat fryers. It would be advantageous to be able to rapidly filter the cooking oil at full cooking temperature.
Deep fat fryer cooking oil is a significant re-occurring cost in the operation of a restaurant, large scale kitchen, donut shop bakery or the like. Likewise disposable cooking oil filters if employed to clean the oil in an attempt to reduce the re-occurring cost of cooking oil themselves represent a re-occurring cost since they are disposable and must be re-purchased, stocked, and discarded under special and relatively expensive handling procedures after one to several filterings. Thus, there still exists significant need for improvements in the field of on-site filtering and extending of the useful life of cooking oil in deep fat fryers for reasons pertaining to economics and the environment.
Additional prior art information pertaining to deep fat fryer oil filtering which may be of interest to the reader can be found in U.S. Pat. No. 3,685,433 issued Aug. 22, 1972 to C. R. Cunningham describing the use of a paper filter for filtering cooking oil; U.S. Pat. No. 5,184,539 issued Feb. 9, 1993 to M. Oiwa describing use of a metal gauze and a ceramic filter for filtering the cooking oil; U.S. Pat. No. 3,968,741 issued Jul. 13, 1976 to A. J. Hunt describing the use of fine paper or cloth filters connected in series to filter cooking oil; and U.S. Pat. No. 3,937,136 issued Feb. 10, 1976 to E. D. Cox describing the use of metal screens for filtering cooking oil.
Prior art information pertaining to metal filters and particularly sinter or diffusion bonded filters can be found in U.S. Pat. No. 2,877,903 issued Mar. 17, 1959 to E. Veres describing use of a cylindrical sintered metal filter for a sump pump; U.S. Pat. No. 2,826,805 issued Mar. 18, 1958 to R. L. Probst et al describing the making of filters from sintered stainless steel particles; U.S. Pat. No. 4,186,100 issued Jan. 29, 1980 to L. H. Mott describing the making of filters from metal particles in a sintering operation; U.S. Pat. No. 3,241,681 issued Mar. 22, 1966 to D. B. Pall describing the making of filters from sintered metal particles; U.S. Pat. No. 2,968,405 issued Jan. 17, 1961 to E. W. Veres describing a sintered metal filter and method of making; and U.S. Pat. No. 2,979,400 Apr. 11, 1961 to H. C. Mouwen describing the making of filter material in a sintering operation. Although none of these patents pertaining to sintered or sinter formed metal filters anticipate the use of sintered stainless steel filters for filtering edible cooking oil of a fat fryer as in the present invention to achieve all of the many significant advantages thereof, they provide details pertaining to the general type of filter element utilized as part of the present invention, and how such filters can be manufactured out of various metals in various shapes and sizes, and in varying porosities for filtering out various sized solid particles from fluids, and with varying sizes and shapes of granular metal particles to be fused to one another in a sintering operation, sometimes referred to as diffusion bonded or bonding, and for this information, U.S. Pat. No. 2,877,903; U.S. Pat. No. 2,826,805; U.S. Pat. No. 4,186,100; U.S. Pat. No. 3,241,681; U.S. Pat. No. 2,968,405; and U.S. Pat. No. 2,979,400 are herein incorporated by reference.